ABSTRACT: This proposed research has several objectives, all based on very promising initial results, including: (a) To synthesize a series of inhibitors of key enzymes that metabolize ammonia, aspartate, or glutamate, namely glutamine synthetase, asparagine synthetase and aspartate transcarbamoylase. These are expected to be potent inhibitors of their respective enzymes, based on their resemblance to tightly bound intermediates or transition states of catalyzed reactions. We propose to apply these analog inhibitors as potential cancer chemotherapeutic agents, as probes of catalytic and regulatory mechanisms, and as affinity ligands. (b) to gain new insights to the regulatory mechanisms of aspartate transcarbamoylase and aspartokinase by equilibrium isotope exhange kinetics, utilizing our newly developed system for uniquely identifiying modifier modes of action. Both activators and inhibitors are known for each. (c) To prove or disprove the possibility of multiple divalent metal ion sites involved in catalysis by mammalian and plant glutamine synthetases. Kinetic data is intriguingly suggestive of two metal ions per subunit.